WASHINGTON, Aug. 7 -- Scientists who believe they have evidence that primitive bacteria once lived on Mars announced Wednesday that they will now try to find cell walls, more complex molecules, and other 'smoking guns' of ancient, extraterrestrial life. The group of researchers, geochemical experts from NASA and several universities, presented their findings at a press conference held with NASA officials at the agency's headquarters. They will also publish them in the August 16 issue of the journal Science. Probing a Martian meteorite in Antarctica, scientists said they found strong circumstantial evidence that single-celled bacteria lived on the red planet at least 3.6 billion years ago. The evidence features a combination of fossil-like structures and organic molecules trapped together within the potato-shaped volcanic Martian rock that landed in the Antarctic 13,000 years ago. After admitting that 'I spent many nights in the lab because I was much too excited to go home,' David McKay of Johnson Space Center in Houston said that he next plans to scrutinize thin sections of the Martian meteorite under a microscope with unprecedented detail. 'We hope to catch these microfossil-like forms,' said McKay, who led the NASA-funded project. 'We should be able to see if these structures contain (cell) membranes, perhaps, or if some of the original cell machinery is left.' Richard Zare of Stanford University in California, who analyzed the meteorite's organic components with his 'homebuilt' laser mass spectrometer, said that he will look for amino acids, the building blocks of proteins -- a convincing signature of life indeed.
It will require such 'smoking guns' to persuade many scientists. 'Keep in mind that at this point we don't even know whether these (fossil-candidate) features were based on carbon,' said paleobiologist William Schopf of the University of California at Los Angeles. In 1993 Schopf reported the discovery of what are currently the oldest microbe fossils on Earth, in western Australia. He said that holding the Mars findings to the same criteria as Earthen samples currently leaves doubt that live organisms, not simply chemical processes, actually made the Martian structures. 'I would be delighted to see...images that showed cell walls,' he said. 'I'd be delighted to see data that show that the population of the organism is different from mineral matter. I'd also like to see some evidence of cell division.' Schopf emphasized that each of these tests are 'do-able now. The technology is available,' he said. Both McKay and Zare hope to have results in a year or so -- perhaps even some insight, if the fossils do turn out to be real -- into whether life began on Mars and Earth independently or started on one planet and migrated to the other. 'We're finding on Earth how robust life is, how it can survive in places that we never thought it could.' Zare said. 'It seems all you need is a volcano, liquid water, and a pinch of carbon.' In response to the find, NASA administrator Daniel Goldin said his agency plans to speed up efforts to retrieve samples from the planet, even if that means sending a manned mission to get the samples. Also Wednesday, President Clinton announced he had asked Vice President Al Gore to convene a bipartisan White House space summit before the end of the year to discuss the future of the space program and to pursue answers to scientific questions raised by this finding. 'The significant purpose of this summit will be to discuss how America should pursue answers to the scientific questions raised by this finding,' he said. 'We are committed to the aggressive plan we have put in place for robotic exploration of Mars,' he said. America's next unmanned mission to Mars, the Mars Pathfinder, is scheduled to lift off from the Kennedy Space Center in November, with a landing slated for next summer. It will be followed by a second mission in December. But those plans were criticized by a report issued just 24 hours earlier by the independent National Research Council. The report warned that current plans for exploring Mars may be too skimpy to find ancient life on the red planet. The council Tuesday evaluated the Mars Surveyor and Pathfinder programs in light of what the report committee called NASA's ''smaller- faster-cheaper' philosophy.' The budget is so tight on the Surveyor missions that they will be able to carry only small landers instead of the advanced rovers that could sample the rock adequately. 'Because evidence for past climate changes and ancient life, if any, is most likely embedded in the rocks, this is a major shortcoming,' said the report. To get around this and other thin patches in the program, the committee recommended that NASA get aggressive in the push to develop miniaturized instruments, and that the agency dovetail its Mars program with international partners, such as the European Space Agency and Japan. Even with improvements in the current plans, the smaller-faster- cheaper philosophy means that NASA will have to endure some flops. The report urged 'a new attitude toward risk management' and 'the ability to accept the occasional but inevitable disappointments.'